This invention relates to a torque feedback transmission and more particularly to a torque feedback transmission with direct couple bypass utilizing operational clutches.
In my patent application entitled "Torque Feedback Transmission" having Ser. No. 649,691 filed on Sept. 12, 1984, now U.S. Pat. No. 4,637,275, there is disclosed and claimed a torque feedback transmission capable of providing perfect coupling between input and output torque and speed without the need for clutching and shifting mechanisms.
In some systems, the output of the hydrostatic transmission is connected either directly, or by fixed gear ratio transmission, to the output shaft. In such a design the rotor of the motor is stationary when the output shaft is stationary. In order to apply a load to the output shaft, sufficient force must exist to overcome the static friction of both the hydraulic motor and the load. In addition, some types of pumps operate inefficiently when they bear a stationary load. In the torque feedback design covered in my aforementioned application, the hydraulic transmission bears only the static friction of the load.
Also, some types of differential units, such as differential cones, can only provide infinite variation over some fixed gear ratio and cannot be directly coupled to a stationary load, whereas, by use of the torque feedback design in my above mentioned application it is possible to couple such devices to a stationary shaft without the use of a clutch, and furthermore, for each state or set of gear ratios, the differential unit may be designed to experience its full range of motion thus resulting in a maximum torque reduction.
In the aforementioned application, a variety of embodiments are disclosed in which a differential unit comprising a fixed displacement hydraulic pump and a variable displacement hydraulic motor are coupled to adjust the torque feedback and accomplish the purposes of the invention. Several of the embodiments disclosed in the application provide for a partial bypass of the differential unit in order to reduce fluid pressures in the pump. Such pressures are of special concern at low speeds and under starting conditions.
In one embodiment of the aforementioned application, there is disclosed a torque splitting arrangement wherein the differential unit is bypassed in such a way that there is a direct coupling from the input to the load of a portion of the torque supplied. In that arrangement, it can be seen that when a stationary load exists at the output shaft all power must flow through the hydrostatic or differential unit, with the accompanying high fluid pressures in the unit and in many cases, depending on the type of pump employed, reduced efficiency.